Manufacture of sound records



Patented Aug. 23, 1938 UNITED STATES PATENT OFFICE N Drawing. Application October 23, 1931, Serial No. 570,755. In Germany September 4, 1929 7 Claims.

My present invention relates to the production of sound records and more particularly to the production of sound records on photographic films. It is a continuation in part of my application Serial No. 479,797, for Non-grained sound film filed September 4, 1930.

One of its objects is to provide a sound record which in reproduction yields sounds with the characteristic stamp of their over-tones by recording the sounds on a photographic film provided with a finest grained highly sensitized or grainless light sensitive layer. Further objects will be seen from the detailed specification following hereafter.

In order to realize an unobjectionable sound record it is necessary to register not only the fundamental tones, but also the superimposed harmonic tones which oscillate much quicker and belong to the range of frequency of about 16,000

to 20,000. It is obvious that such high frequencies can only be registered by means of lightcontrolling apparatus operating without inertia, and the registration of the sound waves is therefore effected by means of, for instance, a Karolus 5 cell, Koenemanns tungsten arc lamps, cathode ray oscillographs or similar devices. The registration with these apparatus is preferably effected through a very narrow slit of a breadth down to 0.0025 mm., whereby it is possible to include a sufficiently wide range of frequency.

It is obvious that such sound records can only be obtained with photographic layers of a very high resolving power, in view of the fact that with the usual velocity of reproduction of talking motion picture films of 456 mm. per second oscillations are to be registered per mm., in which case only 20 to 30 microns are available for each single oscillation. The negative film which has hitherto usually been employed is not suitable because the copies therefrom made on positive film show, according to Sheppard, a grain size up to 5 microns, and, what is Worse, are separated by interspaces of about 30 microns. In U. S. Patents 1,601,078 and 1,756,863 the use of positive film has been proposed for avoiding the groundnoise and for improving the quality of tone, as the positive film is said to yield the same blackening as negative film when subjected to an intense exposure. As the intensity of the recording light-ray cannot be raised at will even in the variable area method, on account of the irradiation and halation, the positive film is'suited only for the registration of at most 5000 oscillations; it is obvious that this kind of film is even less suited for the variable density method where even the slightest light values are to be registered. The use of positive film has therefore no advantage in spite of its grain having only half the size of negative film, since its sensibility amounts only to l/l5 or 1/20 of that of negative film. In order to realize the aforesaid aim, it is necessary to employ an emulsion of a much finer grain, but having the same sensibility, which emulsion, moreover, contains the grains of silver halide in completely homogeneous distribution.

I have found-and this is one of the essential features of my inventionthat perfectly satisfactory sound records are obtainable by using silver halide emulsion layers of high resolving power of the type of positive-, diapositive-, gaslight or Lippmann emulsions, of which the sensibility and especially the sensibility for the light of the artificial source of light used in sound recording is raised by incorporating in the silver halide emulsion layers suitable sensitizing dyes; by these means, according to my experience, the sensibility is increased in such a degree that it is possible to register the quickest variations of light.

sensitizing may be effected according to any of the known processes, for instance, by bathing the silver halide emulsions in solutions of the dyes, or by adding solutions of these materials to the emulsions during their production, whereby other dyes may be added, such as Auramine, Thiofiavine T, which counteract fogging of the sensitized material. Very well suited are finest grained silver halide emulsions comprising a mixture of silver chloride and bromide of the type of gas-light emulsions which after bathing in an aqueous solution of 1 part of Eosine in 20,000 parts of Water or of 1 part of Pinaverdol or Orthochrome in 30,000 parts of water for 4 minutes show a sensibility for the light of an incandescent lamp which has been increased 30 to 50 times. The sensibility of a silver chloride gelatin diapositive emulsion is raised to about times its original sensibility by bathing the same in an aqueous solution of 1 part of Pinaflavol in 10,000 parts of water, whereas the sensibility of a similarly fine grained silver bromide gelatin emulsion is raised only to 20 times its original sensibility. Most of the known sensitizers which have a sensitizing effect for the yellow to the bluish-green region of the spectrum show a similar behavior. An addition of ammonia is helpful as a rule, but impairs mostly the stability, so that this hyper-sensitized film must be consumed very soon. The highest degree of sensibility of these finest grained or almost grainless layers is obtainable by ultrasensitizing in the presence of ammonia and silver salts, if desired, also of hydrogen peroxide. sensitizing may be effected in the following manner:

To 85 cc. of a mixture of equal volumes of water and alcohol there are added cc. of a 2 per cent solution of silver chloride containing the requisite quantity of ammonia to keep the silver chloride dissolved and 5 cc. of an alcoholic solution of the sensitizer (1 part of sensitizing material on 1000 parts of solvent). In this solution the photographic material is bathed for 4 to 5 minutes and dried as quickly as possible in a vacuum. The sensibility of silver chloride gelatin diapositive emulsions is increased by Pinaverdol to about to times its original sensibility; Pinachrome-Violet, Pinacyanol, Pinacyanol-Blue and the other modern sensitizers for the red region of the spectrum show a still better efficiency, but it is necessary to obviate the marked tendency of fogging by the addition of potassium bromide or Phenosafranine or other de-sensitizing materials to the developer. The ammoniacal solution of silver chloride can also be applied without addition of dyestuff before or after bathing the photographic material in the solution of sensitizers or to photographic materials the silver halide emulsion of which has already been sensitized before casting. In the same manner an ammoniacal solution of other silver salts can be employed, for instance, gram of tungstate of silver dissolved in 1000 cc. of an aqueous solution of ammonia of 0.1 per cent to which advantageously 10 cc. of a 3 per cent solu- I tion of hydrogen peroxide have been added. By

these described methods of sensitizing the sensibility of finest grained layers with a grain size of about 0.2 micron can be raised to that of negative films having a medium sensibility; the sensibility of a Lippmann emulsion, especially also that of such emulsions with an increased content of silver, can be raised to the sensibility of positive film. A practically non-grained emulsion which is suitable for being sensitized may be produced as follows:

The two solutions are heated to about 45 C. and mixed. Then the emulsion is divided into two approximately equal parts, whereupon to one of these parts 22.5 cc. of a 10 per cent solution of K181 and 0.5 cc. of a 10 per cent solution of KI are added, and to the other part 30 cc. of a 10 per cent solution of AgNOa. The latter solution is added to the former, then this procedure is repeated three times, and finally 25 grams of dry gelatin are added. By continual heating to 65, the sensibility can be increased, whereupon the material is washed out.

The described mode of sensitizing can likewise be applied to silver halide collodium emulsions for which purpose especially Pinaflavol has proved well suited.

Developing of the gelatin and collodium emulsion layers may be effected physically, whereat in the first case a strongly acid metol-hydroquinone developer or a mixture of ferrous oxalate and silver nitrate may be used; hereby a distinct sound-track is obtainable positioned near the surface. Such sound-tracks are likewise obtained when developing chemically if intensely coloring sensitizers, such as Pinafiavol, have been used, and if the screening effect has been sup ported by use of a blue or violet filter in copying the sound-track. This filter can, as a colored protective layer, be inseparably connected with the photosensitized emulsion layer.

Of great importance is the fact that these finest grained layers which, when unsensitized, are not useful for cinematographic purposes on account of their hard gradation, take a suilicient soft gradation by sensitizing, so that picture and sound-track can be taken and developed together on the same film band. It is obvious that the emulsions can also be used for taking pictures alone which are intended for the production of silent films. The practically non-grained emulsion layers are, however, not suited for this purpose on account of their low sensibility, but they are very well suited for printing together a primary or secondary sound negative and picture negative; when sensitizing has been effected with Pinafiavol, also in this case the sound negative is preferably printed with blue light. In this manner it is possible to manufacture positive talking motion picture films which have a grain size of 0.1 to 0.5 micron and permit to register unobjectionably frequencies up to iii-20,000. The present invention permits therefore to obtain sound films of a quality hitherto unknown.

The finest grained emulsion layers required for the direct photographic recording and transferring are preferably covered with a protecting layer (gelatin, protalbin, casein, dextrin etc.) permeable to the developer; these, or an intermediate layer between the carrier and the emulsion for preventing halation etc. or preferably colored with red or other dyes. It is obvious that the anti-halation dyes must allow an easy decoloring or washing out and must absorb the light for which the halide silver is sensitive. When operating in this manner the record or the optical copies are, if necessary taken from the rear side.

For the production of copies, provided that sufficiently effective are lamps or concentrated light of a mercury lamp is at disposal, other almost grainless light-sensitive materials may be used, e. g., silver halide printing out layers sensi tized by means of Pinafiavol, Rhodamine and so on, or layers containing diazo-compounds which may be developed by vapours of ammonia or by suitable coupling components such as aniline, or by alcoholic alkaline solutions of these ingredients, or I may use cellulose films impregnated with salts of mercury and sensitized by Eosine, Erythrosine and so on.

Silver halide salts suitable for being sensitized may also be produced in a well known manner by precipitating the salts within a layer of gelatin, collodion, ethyl cellulose and so on which are applied to a film base or by precipitating them within the solution intended for casting cellulose films, care being taken that the precipitate is homogeneously distributed throughout the layer. As a carrier for the emulsions photo-sensitized by dyestuffs there may serve paper, aluminium or other opaque materials, requiring reflected light for the intermediate reproduction. The highly sensitized finely grained silver halide emulsion layers can be employed apart from the abovementioned use for copying purposes in a three- III. For the production of a secondary sound negative in an indirect .way from a prime master sound record by photo-electrical transformation.

.Diapositive and similar emulsions, brought to high speed by ultrasensitizing, may. be used for directly recording sounds by sounds of variable density or area in the form of a sound track of about 3 width, in combination with objectives of extremely high light transmitting capacity, for instance, an aplanatic-achromatio condenser (Leitz Works in Wetzlar) having an aperture of (i/0.52 or f/0.32, care being taken for optical contact of the emulsionated side of the cinematographic film with the lens system by means of an immersion fluid.

Highly-sensitive positive film the sensibility of which can easily be increased to 10 times its original value is adapted in the same degree as ordinary positive film for taking a sound-track of 2.5 to 28 mm. breadth which after development serves for the production of sound copies of the same or smaller size.

In order to eliminate the grain of the highly sensitized positive film which may cause trouble, it is recommendable to record the sound Waves as a track of variable density or variable area over the whole breadth of the ultra-sensitized positive film preferably taken at 2 to 3 times higher speed (912 or 1368 mm, per second) than the picture -lm (456 mm. per second). This prime master sound record or its inversion or copy is then proected on a reduced scale by means of spheric and cylindrical lenses to grainless or finest grained highly sensitized emulsion layers so as to form a sound track of 2.8 mm. Width containing registered on the standard length of 456 mm. of one picture area the same number of sound waves as the prime master sound record on 2 to 3 times the length. The secondary sound negative obtained in such a way serves for the production of copies.

III

The finest grained to grainless emulsion layers, highly sensitized by dyestuffs are of the greatest importance for the photo-electrical transformation of a variable density record in a record of variable width, since this latter, alone or together with a picture taken on the same film, may be easier developed than the former.

It is a fundamental observation of the present invention that talking motion picture films of high quality are only obtainable when using not only for taking apparatus working without inertia as used for the variable density method, but also for the transformation, instead of a clumsy shutter, highly sensitive recording apparatus which are suitable for directly recording sounds in a photographic manner (oscillograph, cathodic oscillograph, thread galvanometer, spool galvanometer and so on) which Work without inertia on account of the small mass of the oscillating parts, if the intermediate reproduction is effected about 10 times slower than the original sound recording and on finest grained to grainless silver halide layers highly sensitized by dyestuffs.

- Of course, an original variable area record can be transformed into a variable density record in the same manner, but this mode of proceeding presents no advantages,

The photo-electrical transformation of an original sound record into a finest grained or grainless sound negative of another size which sound negative serves for copying purposes will generally yield better results than the above described optical Method II.

.In any case the original sound record is expediently taken across the whole breadth of a standard positive or diapositive film highly photosensitized by dyestuffs, preferably at a 2 to 3 times higher speed than the picture film. This prime master sound record, or better its inversion or copy, is then slowly led, for instance, past the slit of a repeatingapparatus and causes electric oscillations in a photo-electric or selenium cell which, after being amplified in known manner, controls an oscillograph, Karolus cell or similar apparatus, yielding thus the photographic sound negative on grainless or most finely grained silver halide emulsion layers. Of course, this sound track of about 2.8 mm. width may be produced on an unexposed portion of the picture film, more particularly on the margin between the pictures and the performations, in order to produce by simultaneous development of both the picture and sound record the combined negative or positive of a talking motion picture film. In a similar manner two sound strips running oppositely may occupy the midst of a cinematographic film bearing adjacent the corresponding two series of pictures.

Many other modifications and changes in details will occur to those skilled in the art without departing from the spirit and scope of my invention as defined by the following claims.

What I claim is:

1. In the manufacture of sound films and talking motion picture films the improvement which comprises registering the sound waves on a finely grained to grainless silver halide emulsion layer highly photo-sensitized, and transferring the original sound record thus obtained onto a photographic material provided with a finest grained to grainless light-sensitive layer highly photosensitized by hyperor ultra-sensitizing.

2. In the manufacture of sound films and talking motion picture films the improvement which comprises registering the sound waves on a finely grained to grainless silver halide emulsion layer highly photo-sensitized by hyperor ultra-sensitizing, so as to form a sound track of greater than standard Width and transferring the original sound record thus obtained while photographically reducing the same onto a highly sensitized finest grained to grainless emulsion layer.

3. In the manufacture of sound films and talking motion picture films the improvement which comprises registering the sound waves across the whole breadth on a finely grained to grainless silver halide emulsion layer highly photo-sensitized by hyperor ultra-sensitizing, leading the sound record thus obtained past the slit of a usual repeating apparatus for inducing an electric current undulating in conformity with the variations of the sound record, controlling with this undulating electric current a light controlling apparatus operating without inertia for the production of a sound track of standard size and registering the light variations on a finely grained 7 to grainless silver halide emulsion layer highly photo-sensitized.

4. In the manufacture of sound films and talking motion picture films the improvement which comprises registering the sound waves on a finely grained to grainless silver halide emulsion layer highly photo-sensitized by hyperor ultra-sensitizing, and printing by contact onto a finely grained to grainless. silver halide emulsion layer highly photo-sensitized by hyperor ultra-sensitizing.

5. In the manufacture of sound films and talking motion picture films the improvement which comprises registering a sound and picture record together on a finely grained to grainless silver halide emulsion layer highly photo-sensitized by hyper or ultra sensitizing.

6. In the manufacture of sound films and talking motion picture films the improvement which comprises registering the sound waves on a photographic material provided with a finely grained to grainless silver halide emulsion layer highly photo-sensitized by hyper or ultra sensitizing, with 5 a anti-halation layer and with a colored protective layer.

7. In the manufacture of sound films and talking motion picture films the improvement which comprises registering the sound waves on a finely 10 selected from the group consisting of diazo-com- 15 pounds and sensitized mercury salts.

CHARLES SCHINZEL. 

